Influence of no-tillage and organic mulching on tomato (Solanum Lycopersicum L.) production and nitrogen use in the mediterranean environment of central Italy

Scientia Horticulturae 130 (2011) 588–598

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Influence of no-tillage and organic mulching on tomato (Solanum Lycopersicum L.) production and nitrogen use in the mediterranean environment of central Italy Enio Campiglia ∗ , Roberto Mancinelli, Emanuele Radicetti Dipartimento di Scienze e Tecnologie per l’Agricoltura, le Foreste, la Natura e l’Energia, Università della Tuscia, via S.Camillo de Lellis, 01100 Viterbo, Italy

a r t i c l e

i n f o

Article history: Received 31 March 2011 Received in revised form 4 August 2011 Accepted 8 August 2011 Keywords: Cover crops Organic mulches No-tillage Nitrogen use Tomato

a b s t r a c t In conservation tillage systems based on legume mulches it is important to optimize N management strategies. The present study evaluated the effect of some winter legume cover crops converted into mulches on the following no-tillage tomato (Solanum Lycopersicum L.) yield, tomato nitrogen uptake, tomato use efficiency (NUE), soil nitrate and the apparent N remaining in the soil (ARNS) in a Mediterranean environment. Field experiments were carried out from 2002 to 2004 in a tomato crop transplanted into: four different types of mulches coming from winter cover crops [hairy vetch (Vicia villosa Roth.), subclover (Trifolium subterranem L.), snail medic (Medicago scutellata L. Miller), and Italian ryegrass (Lolium multiflorum Lam.)]; a conventional tilled soil (CT); and a no-tilled bare soil (NT). All treatments were fertilized with three different levels of nitrogen (N) fertilizer (0, 75, and 150 kg N ha−1 ). Cover crop aboveground biomass at cover crop suppression ranged from 4.0 to 6.7 t ha−1 of DM and accumulated from 54 to 189 kg N ha−1 , hairy vetch showed the highest values followed by subclover, snail medic and ryegrass. The marketable tomato yield was higher in no-tilled legume mulched soil compared to no-tilled ryegrass mulched soil, CT, and NT (on average 84.8 vs 68.7 t ha−1 of FM, respectively) and it tended to rise with the increase of the N fertilization level. A similar trend was observed on tomato N uptake. Hairy vetch mulch released the highest amount of N during tomato cultivation followed by subclover, snail medic, and ryegrass (on average 141, 96, 90 and 33 kg N ha−1 ). The tomato NUE tended to decrease with the increase of the N fertilization rates, it ranged from 39 to 60% in no-tilled legume mulched soil and from −59 to 30% in no-tilled ryegrass mulched soil when compared to the CT. The soil NO3 -N content and the ARNS was always higher in the soil mulched with legumes compared to the soil mulched with ryegrass and in NT and CT. This study shows that direct transplanting into mulches coming from winter legume cover crops could be useful for improving the yield and the N-uptake in a no-tillage tomato crop. Furthermore, considering the high N content in the upper soil layer and the remaining N content in the organic mulch residues after tomato harvesting, there is a large amount of N potentially available which could be immediately used by an autumn–winter cash crop. © 2011 Elsevier B.V. All rights reserved.

1. Introduction In recent years, interest in sustainable agricultural practices has grown with the aim of reducing production costs and potential environmental impacts of pesticides and mineral fertilizers (Gilbert et al., 2009; Guarda et al., 2004). Among the nutrients supplied to the crops, nitrogen (N) is frequently considered the main key limiting factor responsible for lower productivity, especially in organic farming systems (Möller et al., 2008). In fact mineral N fertilizers have boosted crop yield, in intensive agricultural systems (Crews and Peoples, 2004) but its incorrect use often leads to a low nitrogen use efficiency and serious N loss with potential risks of polluting the environment such as high production of nitrous oxide, which is a

∗ Corresponding author. Tel.: +39 761 357538; fax: +39 761 357558. E-mail address: [email protected] (E. Campiglia). 0304-4238/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2011.08.012

powerful greenhouse gas, and leaching of nitrate in groundwater (Shi and Yu, 2008; Jensen and Hauggaard-Nielsen, 2003). Therefore, it needs to develop and/or improve N agricultural management practices in order to reduce environmental risk and enhance N use efficiency (Sainju and Singh, 2008; Kuo and Jellum, 2002). The introduction of cover crops in cropping systems could be a suitable practice for recycling and using N from natural sources, such as the N content in the residues of the previous crop and the N fixed biologically from the atmosphere. For this concern, legume cover crops are considered an important tool in N management, because they can be used to accumulate nitrogen during the un-cropped period and to supply N during the cultivation of the following main crop (Möller and Reents, 2008; Hartwig and Ammon, 2002). Nfixation measurements show that the legume cover crops used in annual cropping systems can supply from 50 to 250 kg N ha−1 (Peoples et al., 1995), stored in below-ground and above-ground biomass, which represent a potentially valuable source of N for

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replenishing soil N pools (Peoples and Craswell, 1992). A successful N cover crop residue management strategy is to synchronize the release of inorganic N from the cover crop biomass with N demand by the subsequent cash crop so that cover crop derived N is retained in the system, and N loss via leaching and denitrification of the mineralized cover crop derived N is minimized (Jackson, 2000). In the Mediterranean area, winter legume cover crops are sown in late summer, they grow during the autumn and winter, and are generally suppressed in spring before the summer crop planting (Coppens et al., 2006). The management of legume cover crop residues before the succeeding crop planting is one important part of the management of the whole production system, which deserves more attention, in order to synchronize N mineralization from the residues and the crop demand (Snapp and Borden, 2005). The rate of N mineralization strongly depends on environmental factors (Cabrera et al., 2005), on the chemical and physical characteristics of the residues (Thomsen and Christensen, 1998), and on soil organisms (Hauggaard-Nielsen et al., 1998). Generally, after cover crop suppression, the residues are plowed into the soil as green manure. The incorporation into the soil of legume cover crop biomass, characterized by a low C:N ratio, frequently results in a rapid release of mineral N shortly after plowing and planting the succeeding main crop when its N uptake is still minimal (Drinkwater et al., 2000). Another option after cover crop suppression is to leave the residues on the soil surface as organic dead mulches in no-till crop production systems (Abdul-Baki et al., 1997; Teasdale et al., 2008). The placement of cover crop residues on the soil surface in no-tillage systems slows down the decomposition rate of residues compared to green manure strategy due to its reduced contact with soil and soil organisms, therefore it reduces N release (Sainju et al., 2002). Furthermore, the management of cover crop residues left on the soil surface, such as untouched, mowed, chopped and grounded, could modify the speed of the mineralization process as a consequence of the N release (Campiglia et al., 2010a; Kruidhof et al., 2008). In recent studies, the aboveground biomass of different winter cover crops placed in strips as organic dead mulches in no-till systems has been proposed as a means for N supply and yield improvement of the following summer vegetable crops such as tomato and pepper (Campiglia et al., 2010b, 2011). Tomato is one of the most important vegetables in the Mediterranean environment in terms of planted area and crop value with high N requirements. The recommended N-fertilizer rate for tomato is up to 220 kg ha−1 (Zotarelli et al., 2009). Conventional practices of tomato cultivation, including soil plowing and excessive N fertilization, could degrade soil, and soil water quality (Sainju et al., 2001). Although, there is a large amount of literature on cover cropping and tillage effects on tomato responses (Sainju et al., 2002), there is little information on the effects of winter cover crops converted into dead mulches on no-till tomato performance and tomato N use. The objective of this study was to investigate the effects of several annual winter legume cover crops used as organic mulches for no-tillage tomato production in a Mediterranean area of Central Italy on: (1) tomato yield, (2) tomato N uptake, (3) tomato N-use efficiency, (4) N supply from legume cover crop residues, (5) NO3 -N soil content during cover crop-tomato sequences, and (6) apparent N remaining in the soil after tomato harvesting.

2. Materials and methods 2.1. Field site description The experiment was carried out at the experimental farm of Tuscia University in Viterbo, Italy (lat. 42◦ 26 , long. 12◦ 40 , alt. 310 m a.s.l.) from September 2002 to August 2004. The mean annual tem-

589

perature of the area is 14.3 ◦ C and the mean annual precipitation is approximately 750 mm. The climate of the region is a typical Mediterranean climate with rainfall predominately in the period October–April. A cover crop–tomato sequence was carried out for two cropping seasons (2002/2003 and 2003/2004) in two nearby fields previously kept fallow. The soil characteristics prior to sowing the cover crops (0–30 cm layer), which did not significantly differ in the two nearby fields, were: 16.0% clay, 20.5% silt, and 63.5% sand; pH 6.8. (H2 O, 1:2.5); soil organic matter content 1.7% (Lotti); and soil total nitrogen 0.15% (Kjeldahl). 2.2. Experimental design and treatments The treatments consisted in: (a) six soil managements [no-tilled soil mulched with hairy vetch (Vicia villosa Roth.) (NTHV), no-tilled soil mulched with subclover (Trifolium subterraneum L.) (NTSC), notilled soil mulched with snail medic (Medicago scutellata L. Miller) (NTSM), no-tilled soil mulched with Italian ryegrass (Lolium multiflorum Lam.) (NTIR), no-tilled bare soil (NT), and conventional tilled soil (CT)]; (b) three levels of nitrogen fertilization applied to the tomato crop (0, 75, and 150 kg ha−1 of nitrogen). The experimental design was a split-plot (6 soil management treatments × 3 N fertilization levels) with four replicate blocks, where the soil management was the main factor and the level of nitrogen fertilization the split factor. The main plot size was 108 m2 (6 m × 18 m), and the sub-plot size was 36 m2 (6 m × 6 m). 2.3. Farming practices In both years (2002/2003 and 2003/2004), the soil was plowed in the first week of September to a depth of 30 cm, then, it was fertilized with 100 kg ha−1 of P2 O5 , as triple superphosphate, and harrowed in order to break the soil clods into smaller pieces for seed bed preparation. Seeds of hairy vetch (var. Capello), subclover (var. Antas), snail medic (var. Kelson), and Italian ryegrass (var. Asso) were hand sown and slightly buried by gentle harrowing on September 12th, 2002 and September 26th, 2003. In both years the seed rate of cover crops was 60, 30, 50, and 30 kg ha−1 for hairy vetch, subclover, snail medic, and Italian ryegrass, respectively. In the CT and NT plots, the soil was kept bare throughout the cover crop growing season by chemical means (glyphosate applied twice), when the weed seedlings started to emerge. On May 5th, 2003 and May 12th, 2004 the above-ground biomass of cover crops was mowed to around 3 cm above the soil surface and arranged in strips with an hay-conditioner machine. The hay-conditioner cut the cover crop above-ground biomass to a width of 2.0 m and arranged the residues in order to obtain mulch strips about 80 cm wide, 5 cm thick, and 120 cm apart (Campiglia et al., 2010b) used as transplanting beds for tomato seedlings. In the CT and NT plots, the transplanting bed was prepared by a rotary harrow and by a herbicide treatments (glyphosate) for killing the weeds, respectively. Both soil management treatments were applied at the same time as the organic mulch arrangement. About 1 week after bed preparation, processing tomato seedlings (Solanum Lycopersicum L.) of the “Caspar” variety were transplanted by hand into the mulch layer with minimal disturbance, and in CT and NT treatments on May 13th, 2003 and May 20th, 2004. The tomato seedlings were arranged in paired rows 0.4 m wide, with a distance between the rows of 1.60 m. The distance between the tomato plants in the rows was 33 cm, and the tomato density was 3 plants m−2 . The same geometry was maintained in all soil management treatments. Irrigation water was supplied with drip irrigation tape installed over the cut mulch and/or soil surface in the middle of the paired rows. The amount of water inputs was determined by evapotranspiration estimated by class A pan evaporimeter and converted by crop coefficients during the tomato growing period (Allen et al., 1998). Drip

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irrigation started immediately after tomato transplanting reintegrating the 90% of maximum evapotranspirated water and it was stopped 2 weeks before tomato harvesting when the fruits began to redden. The N fertilizer (0, 75, and 150 kg N ha−1 hereafter called N0 , N75 , and N150 , respectively) was applied through ferti-irrigation as urea twice, half the amount on June 10th and the remaining N on July 10th in 2003 and June 21st and July 12th in 2004, respectively. All plots were maintained weed-free by hand-weeding whenever necessary both within and between the tomato paired rows. Repeated copper treatments were applied during tomato growing seasons in order to control tomato diseases. The tomato fruits were harvested on August 25th, 2003 and August 30th, 2004. 2.4. Sampling and measurement In both years, at cover crop suppression, the above-ground biomass of cover crops was hand-clipped at the soil surface and collected using a 100 cm × 100 cm quadrat, at tomato harvesting the mulch residues were collected using a 80 × 50 rectangle placed in the centre of the tomato row. The biomass samples were oven dried at 70 ◦ C until constant weight and their N content was determined (Kjeldahl method). At tomato harvesting, 12 tomato plants were cut manually about 2 cm above the soil surface in the two middle rows of each plot in order to determine: the fresh weight of marketable fruits and their number, the straw weight (over dried at 70 ◦ C until constant weight), and the marketable fruits and straw N content (Kjeldahl method). The total N accumulation was calculated by multiplying the biomass dry weight by the corresponding N concentration. In both years in all plots, 6 soil cores, 47 mm diameter and 50 mm high each, were collected using a soil corer, in order to measure soil dry bulk density at depths of 0–30 cm. At the same time 10 soil samples were taken in the 0–30 cm layer in all plots according to the main soil tillage management and mixed together, NH4 -N and NO3 -N concentration was determined with the colorimetric method (Anderson and Ingram, 1993; Cataldo et al., 1975). The soil samples were collected in both years at cover crop sowing, at tomato transplanting, and at tomato harvesting in all N fertilization level plots. NH4 -N was determined only at tomato transplanting. During tomato cultivation, the soil samples were taken from the centre of the tomato rows removing the mulch layer where present. Tomato N uptake, residual NO3 -N, and N use efficiency (NUE) were calculated with the following formulas as reported by Gao et al. (2009): A = (a × b) + (c × d) where A is N uptake (kg N ha−1 ), a is the marketable tomato yield (kg ha−1 of DM), b is the N concentration of marketable tomato fruits (g of N/100 g of dry tomato fruit), c is the tomato straw yield (kg ha−1 of DM), and d is the N concentration of tomato straw (g of N/100 g of dry tomato straw). C=

h×i×p 10

where C is the total residual NO3 -N (kg N ha−1 ), h is the soil depth (cm), i is the soil bulk density (g cm−3 ), and p is the nitrate concentration of the soil samples (mg NO3 -N kg−1 dry soil). (e − f ) × 100% B= g where B is N use efficiency (NUE, %), e is N uptake of tomato in mulched treatments with and without the application of N (kg N ha−1 ), f is N uptake of tomato in CT or NT treatments without N fertilizer applied, and g is the N supplied to the tomato crop (kg N ha−1 of N fertilizer + N released from cover crop above-ground biomass between tomato planting and harvesting).

The apparent N remaining in the soil (ARNS) after tomato harvesting was calculated using the following formula (Kramberger et al., 2009): ARNS = (Ncc + Nmin + Nfert ) − Nuptake where ARNS is the apparent remaining N in the soil (kg ha−1 of N), Ncc is the N in the cover crops (kg ha−1 of N), Nmin is the soil mineral N (NH4 -N + NO3 -N) at tomato transplanting (kg ha−1 of N), Nfert is the N added with fertilization (kg ha−1 of N), and Nuptake is the N taken up in the total above-ground biomass of tomato crop (kg ha−1 of N). 2.5. Statistical analysis Analysis of variance (ANOVA) was carried out using the JMP statistical software (SAS Institute, 2000). The analysis of variance was carried out for the 2-year period, considering the year as a random effect. A split plot experimental design was adopted for the cover crop characteristics, soil NO3 -N content at cover crops sowing and at tomato transplanting, where the year was considered as the main factor and the cover crop as the split factor. A split–split plot experimental design was adopted for tomato characteristics, soil NO3 -N content at tomato harvesting, NUE and ARNS, where the year was treated as the main factor, soil management the split factor and N fertilization rate as the split–split factor. Arcsine-square root transformation was performed, when the variances of data sets were heterogeneous (Bartlett’s test, Gomez and Gomaez, 1984). The data reported in the tables were back transformed. Mean values of treatments were compared using Fisher’s protected LSD test at the 0.05 probability level. 3. Results 3.1. Weather conditions The weather conditions observed during the experimental period differed between the two cover crop-tomato sequences (Fig. 1), however the abundant rainfall observed in both years after sowing determined a regular germination of winter cover crops in all plots. The total rainfall through the cover crop growing period was lower in 2002/2003 than in 2003/2004 (483 vs 650 mm, respectively), and these two values were lower and higher respectively, compared to historical trend (504 mm). In the same periods the average daily temperature was generally lower in 2003/2004 compared to 2002/2003, especially in January, February, and March 2004 when the minimum temperature dropped below 0 ◦ C several times (Fig. 1). In both years, throughout the tomato cultivation period rainfall was mainly concentrated immediately after tomato transplanting, and it was higher in 2004 compared to 2003 (164 vs 59 mm, respectively). In the same period, the average air temperature was generally higher in 2003 than 2004 (24.1 vs 19.1 ◦ C, respectively), especially in June, July, and August when the maximum air temperature frequently went over 30 ◦ C. 3.2. Cover crop and mulch biomass and nitrogen accumulation The growing season of the cover crops (September–May) lasted for 243 and 227 days in 2002/2003 and 2003/2004, respectively. At cover crop suppression, the hairy vetch was at the late flowering stage, the subclover and the ryegrass were at the end of the ripe fruit stage, while the snail medic had already set the seeds. The total above-ground biomass of the cover crops was significantly influenced by the year, it was higher in 2002/2003 compared to 2003/2004 growing season (6.08 vs 4.92 t ha−1 of

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Fig. 1. Rainfall, minimum and maximum average air temperatures at 10-day intervals at the experimental site, from September 2002 to September 2004.

DM, respectively). Generally, in 2002/2003 the hairy vetch and the snail medic gave the highest above-ground biomass (on average 6.69 t ha−1 of DM), followed by subclover (5.73 t ha−1 of DM), and ryegrass (5.20 t ha−1 of DM) (Table 1). In 2003/2004 the cover crop above-ground biomass was higher in hairy vetch and subclover (on average 5.35 t ha−1 of DM), intermediate in ryegrass (4.95 t ha−1 of DM), and lower snail medic (4.04 t ha−1 of DM). Among the cover crops, only the hairy vetch and the snail medic showed a significant reduction of the above-ground biomass between the years (6.72 and 6.65 t ha−1 of DM vs 5.43 and 4.04 t ha−1 of DM, in 2002/2003 and 2003/2004, respectively), while, it was similar in subclover and ryegrass (on average 5.50 and 5.08 t ha−1 of DM, respectively). There was a significant interaction cover crop × year on the total N content accumulated in the above-ground biomass of the cover crops (Table 1). In both years, hairy vetch showed the highest N accumulation (on average 164 kg N ha−1 ). However, in 2002/2003 the N accumulated was higher in hairy vetch, intermediate in subclover and snail medic, and it was lower in ryegrass (on average 189, 135, and 55 kg N ha−1 , respectively), while in 2003/2004, the N accumulated in the cover crop above-ground biomass was higher in hairy vetch and subclover compared to snail medic and ryegrass (on average 126 vs 73 kg N ha−1 , respectively). Hairy vetch and snail medic showed a significant reduction of N accumulation in the above-ground biomass in 2003/2004 compared to 2002/2003 (−27% and −38%, respectively).

The cover crop above-ground biomass was converted into mulch which was reduced throughout the tomato cultivation period. Generally, at tomato harvesting the legume mulches showed a higher reduction rate compared to ryegrass (on average 70.9 and 46.1%, respectively) although in 2003 hairy vetch showed the highest reduction rate (76.3%), followed by subclover and snail medic (on average 63.4%), while in 2004, the reduction of mulch was similar among the legumes (on average 74.1%). Throughout tomato cultivation the mulches released an abundant amount of N which was higher in hairy vetch, even if it was lower in 2003 compared to 2004 (117 vs 165 kg N ha−1 , respectively), intermediate in subclover and snail medic (on average 93 kg N ha−1 , respectively), and lower in ryegrass mulch (on average 33 kg N ha−1 ) (Fig. 2). At tomato harvesting the N content in the organic mulch was significantly lower compared to that observed at tomato planting. It ranged between 31 and 16 kg N ha−1 , and was similar in all mulches except for snail medic and subclover which showed a higher N content in 2003 (on average 31 kg N ha−1 ), and a lower N content in 2004 (on average 17 kg N ha−1 ) (Fig. 2). 3.3. Tomato characteristics The analysis of variance of the tomato yield and its characteristics showed significant differences between the years, soil managements, and the N fertilization levels, while there were not

Table 1 The effect of interaction of the cover crop × year on cover crop above-ground biomass and its nitrogen accumulation at cover crop suppression and on mulch reduction at tomato harvesting. Values belonging to the same variable followed by the same letter are not significantly different according to LSD (0.05), in rows for year (upper case letter) and columns for cover crop (lower case letter). Cover crop

Cover crop above-ground biomass 2002/2003

2003/2004

t ha−1 of DM Ryegrass Snail medic Subclover Hairy vetch Cover crop (A) Year (B) A×B

Cover crop nitrogen accumulation 2002/2003

2003/2004

kg ha−1

5.20 bA 6.65 aA 5.73 abA 6.72 aA

4.95 abA 4.04 bB 5.27 aA 5.43 aB ns * *

Mulch reduction at tomato harvesting 2003

2004

%

54.48 cA 139.71 bA 129.70 bA 189.27 aA

58.39 bA 87.17 abB 112.69 aA 138.70 aB ** ** *

49.75 cA 62.25 bA 64.50 bB 76.25 aA

42.50 bA 71.25 aA 74.50 aA 76.50 aA ** ns *

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Fig. 2. The effect of interaction of the soil management × year on N released from organic mulch from tomato planting to tomato harvesting and remaining N in the organic mulch at tomato harvesting. Values belonging to the same variable followed by the same letter are not significantly different according to LSD (0.05).

significant interactions among the treatments except for cover soil management × fertilization level for nitrogen content in tomato fruits (Table 2). The marketable fruit yield was higher in 2003 than in 2004 [82.89 vs 70.55 t ha−1 of fresh matter (hereafter called FM), respectively]. Generally, tomato in NTHV, NTSC and NTSM showed a higher marketable yield in comparison to NTIR, CT and NT treatments (on average 84.76 vs 68.68 t ha−1 of FM, respectively). The highest nitrogen fertilization level (hereafter called N150 ) showed the highest marketable fruit yield, followed by intermediate nitrogen fertilization level (hereafter called N75 ), and unfertilized tomato crop (hereafter called N0 , 85.94, 78.06, and 66.17 t ha−1 of FM, respectively). The number of marketable fruits and the tomato straw weight followed a similar trend already mentioned for tomato yield (Table 2). Generally, N content in the marketable fruits was higher in NTHV, NTSC and NTSM regardless of the level of the N fertilization, except for NTSM with N0 fertilization level where it was lower (on average 2.72 and 2.45%, respectively, Fig. 3). In NTIR, CT and NT treatments the N content in the mar-

ketable fruits was always lower than in the legume mulches and it tended to rise with the increase of the N fertilization levels (on average 1.96%, 2.12%, and 2.39% with N0 , N75 , and N150 , respectively), even if statistical differences among N0 and N75 treatments were not observed (Fig. 3). The nitrogen content in tomato straw differed with the year and it was higher in 2003 than in 2004 (2.17% vs 2.00%, respectively), moreover it was higher in NTHV and NTSC, intermediate in NTSM, and lower in NTIR, CT and NT (on average 2.27%, 2.20%, and 1.93%, respectively). As expected the N content in tomato straw rose with the increase of the nitrogen fertilization rate (on average 1.97%, 2.10%, and 2.19% with N0 , N75 , and N150 , respectively, Table 2). 3.4. Soil NO3 -N and N budget The soil nitrate concentrations (NO3 -N) at cover crop sowing, at tomato transplanting, and at tomato harvesting regarding the different treatments are reported in Table 3. Generally, the soil

Table 2 Mean effects of year, soil management, and nitrogen fertilization level on marketable fruit yield, marketable fruits, and straw weight of tomato crop, and nitrogen content in both tomato marketable fruits and tomato straw. Values belonging to the same variable and treatment followed by the same letter are not significantly different according to LSD (0.05). Treatment

Marketable fruit yield t ha−1 of FM

Marketable fruits n◦ m−2

Straw weight t ha−1 of DM

N content fruits % of DM

N content straw % of DM

82.89 a 70.55 b

47.54 a 27.14 b

2.49 a 2.22 b

2.51 a 2.33 b

2.17 a 2.00 b

Year 2003 2004 Soil management NTIR NTSM NTSC NTHV CT NT N fertilization N0 N75 N150

67.15 b 82.57 a 84.09 a 87.63 a 71.00 b 67.90 b

30.10 b 39.72 a 43.73 a 44.60 a 32.81 b 33.06 b

2.16 b 2.50 a 2.56 a 2.68 a 2.18 b 2.05 b

2.13 c 2.60 b 2.68 ab 2.80 a 2.20 c 2.14 c

1.93 c 2.20 b 2.23 ab 2.31 a 1.96 c 1.90 c

66.17 c 78.06 b 85.94 a

31.14 c 38.70 b 42.18 a

2.03 c 2.32 b 2.71 a

2.29 c 2.43 b 2.56 a

1.97 c 2.10 b 2.19 a

Soil management (A) Fertilization (B) A×B Year (C) A×C B×C A×B×C

** ** ns ** ns ns ns

** ** ns ** ns ns ns

** ** ns ** ns ns ns

** ** * ** ns ns ns

** ** ns ** ns ns ns

NTIR, no tillage Italian ryegrass; NTSM, no tillage snail medic; NTSC, no tillage subterranean clover; NTHV, no tillage hairy vetch; CT, conventional tillage; NT, no tillage. N0 , N75 , and N150 are the nitrogen levels of 0, 75, and 150 kg ha−1 of N applied. *, **, ns: significance at p ≤ 0.05, p ≤ 0.01 or p > 0.05, respectively.

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Fig. 3. The effect of interaction of the soil management × N fertilization level on N content in marketable tomato fruits at tomato harvesting. Means followed by the same letter are not significantly different according to LSD (0.05). NTIR, no tillage Italian ryegrass; NTSM, no tillage snail medic; NTSC, no tillage subterranean clover; NTHV, no tillage hairy vetch; CT, conventional tillage; NT, no tillage.N0, N75, and N150 are the nitrogen levels of 0, 75, and 150 kg ha−1 of N applied.

nitrate concentration increased gradually over time showing differences among soil management treatments. As expected at cover crop sowing there were differences in soil NO3 -N concentration only between the years (19 and 17 mg NO3 -N kg−1 dry soil in 2002/2003 and 2003/2004 respectively), while at tomato transplanting significant differences in soil NO3 -N concentration among the soil management treatments were observed. The highest values were observed in NTHV and NTSM, followed by NTSC, CT and NT, and the lowest value was found in NTIR (on average 23, 20, and 15 mg NO3 -N kg−1 dry soil, respectively). The largest differences of NO3 -N content, as a function of soil management and nitrogen fertilization level, were observed at tomato harvesting. Generally, in the absence of N fertilization (N0 ), NTHV showed the highest soil NO3 -N content followed by NTSM, and NTSC while NTIR, CT, and NT had the lowest soil NO3 -N content (on average 29, 26, and 20 mg NO3 -N kg−1 dry soil, respectively). At the intermediate

N fertilization level (N75 ), the soil NO3 -N content increased, and the legume mulches showed a higher NO3 -N content compared to NTIR, CT, and NT treatments (on average 27 vs 21 mg NO3 N kg−1 dry soil, respectively). A higher soil NO3 -N content was also observed at the highest N fertilization level (N150 ) even if the trend was similar to that already observed at N75 fertilization level. In fact NTHV, NTSC, and NTSM showed higher values compared to the other soil treatments (on average 28 and 24 mg NO3 -N kg−1 dry soil, respectively). The apparent N remaining in the soil (ARNS) at tomato harvesting was significantly affected by the N fertilization level and there was an interaction soil management × year. ARNS was higher in N150 , intermediate in N75 , and lower in N0 (on average 143, 100, 56 kg N ha−1 of N, respectively). Among the soil management treatments the highest value was observed in NTHV (on average over the years 172 kg ha−1 of N), even if all legume mulches showed an ARNS higher than NTIR, and NT in both years

Table 3 Mean effects of soil management at cover crop sowing and at tomato transplanting, and interaction effect of soil management × nitrogen fertilization level at tomato harvesting on soil nitrate content in the 0–30 cm soil layer. Values belonging to the same variable followed by the same letter are not significantly different according to LSD (0.05), in rows for nitrogen fertilization level (upper case letter) and columns for soil management (lower case letter). Soil management

Soil NO3 -N content at cover crops sowing

Soil NO3 -N content at tomato transplanting

Soil NO3 -N content at tomato harvesting

mg NO3 -N kg−1 dry soil

mg NO3 -N kg−1 dry soil

N0

N75 −1

mg NO3 -N kg NTIR NTSM NTSC NTHV CT NT

17.89 a 17.16 a 19.00 a 17.13 a 17.49 a 18.49 a

14.88 c 22.22 a 21.59 ab 23.66 a 19.85 b 18.33 b

Soil management (A) Fertilization (B) A×B Year (C) A×C B×C A×B×C

ns – – * ns – –

* – – * * – –

19.92 cA 26.50 abA 25.11 bA 28.51 aA 18.82 cB 19.83 cB

N150

dry soil 20.62 bA 26.59 aA 25.75 aA 27.31 aA 21.24 bB 19.91 bB

22.51 bA 27.03 aA 27.35 aA 28.99 aA 24.06 bA 23.98 bA

** ** * * ns ns ns

NTIR, no tillage Italian ryegrass; NTSM, no tillage snail medic; NTSC, no tillage subterranean clover; NTHV, no tillage hairy vetch; CT, conventional tillage; NT, no tillage. N0 , N75 , and N150 are the nitrogen levels of 0, 75, and 150 kg ha−1 of N applied. *, **, ns: significance at p ≤ 0.05, p ≤ 0.01 or p > 0.05, respectively.

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Fig. 4. The effect of interaction of the soil management × year on apparent remaining N in the soil (ARNS) at tomato harvesting. Means followed by the same letter are not significantly different according to LSD (0.05). NTIR, no tillage Italian ryegrass; NTSM, no tillage snail medic; NTSC, no tillage subterranean clover; NTHV, no tillage hairy vetch; CT, conventional tillage; NT, no-tillage.

(on average 149, 77, and 36 kg ha−1 of N, respectively). Generally ARNS was similar in both years in each soil management treatment except for NT where it was lower in 2003 compared to 2004 (Fig. 4). 3.5. N supply, N uptake and residual N in tomato crop The analysis of variance of N dynamics in the tomato crop showed significant differences between year, soil management, and N fertilization level (Table 4), while there were not significant interactions among the treatments, except for soil management × year in both N supply to tomato and residual N (data not shown). The N supply to tomato, the total tomato N uptake, and the residual N

were higher in 2003 compared to 2004 (143, 182, and 73 vs 128, 142, and 59 kg N ha−1 , respectively). The N supply to tomato was the highest in NTHV (216 kg N ha−1 ), followed by NTSC and NTSM (on average 168 kg N ha−1 ), NTIR (108 kg N ha−1 ), and it was the lowest in CT and NT (75 kg N ha−1 ). A similar trend was observed in the total tomato N uptake, in fact it was the highest in NTHV, followed by NTSC, NTSM, NTIR, CT, and NT (on average 207, 192, 182, 130 kg N ha−1 respectively). The residual N measured after tomato harvesting was the highest in legume mulches, intermediate in NTIR, and it was the lowest in CT and NT (on average 82, 65, and 41 kg N ha−1 , respectively). The N supply to tomato, the total tomato N uptake, and the residual N rose with the increase of N fertilizer applied to the tomato crop (Table 4).

Table 4 Mean effects of year, soil management, and N fertilization level on N supply (N from cover crop + N from fertilizer) to tomato, tomato N uptake (N tomato fruits + N tomato straw), and residual N (N content in the residual mulch + N content in tomato straw) at tomato harvesting. Values belonging to the same variable and treatment followed by the same letter are not significantly different according to LSD (0.05). Treatment

Tomato N supply kg N ha−1

Total tomato N uptake kg N ha−1

Residual N kg N ha−1

142.58 a 127.55 b

181.75 a 142.31 b

72.48 a 58.83 b

Year 2003 2004 Soil management NTIR NTSM NTSC NTHV CT NT N fertilization N0 N75 N150

107.93 c 164.83 b 171.41 b 216.23 a 75.00 d 75.00 d

128.01 c 182.22 b 192.35 ab 207.22 a 134.97 c 127.41 c

65.38 b 78.91 a 82.00 a 84.85 a 43.16 c 39.62 c

60.07 c 135.06 b 210.06 a

131.15 c 162.30 b 192.64 a

56.34 c 64.97 b 75.64 a

Soil mamagement (A) Fertilization (B) A×B Year (C) A×C B×C A×B×C

** ** ns ** ** ns ns

** ** ns ** ns ns ns

** ** ns ** * ns ns

NTIR, no tillage Italian ryegrass; NTSM, no tillage snail medic; NTSC, no tillage subterranean clover; NTHV, no tillage hairy vetch; CT, conventional tillage; NT, no tillage. N0 , N75 , and N150 are the nitrogen levels of 0, 75, and 150 kg ha−1 of N applied. *, **, ns: significance at p ≤ 0.05, p ≤ 0.01 or p > 0.05, respectively.

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Fig. 5. Effect of interaction of the soil management × N fertilization level on N use efficiency (NUE) of tomato in mulched treatments compared to conventional tillage and no-tillage without N fertilizer. Values belonging to the same variable and treatment followed by the same letter are not significantly different according to LSD (0.05). NTIR, no tillage Italian ryegrass; NTSM, no tillage snail medic; NTSC, no tillage subterranean clover; NTHV, no tillage hairy vetch; CT, conventional tillage; NT, no tillage. N0, N75, and N150 are the nitrogen levels of 0, 75, and 150 kg ha−1 of N applied.

3.6. N use efficiency The results of N use efficiency (NUE) of tomatoes grown on different mulches compared to CT and NT soil management treatments without N fertilizer are presented in Fig. 5. The NUE presented a large variation depending on mulch type and N fertilization level (from −59 to 69%). It was always higher when compared to NT tomato in respect to CT and it decreased when the N fertilization level rose, except in NTIR. The NUE of tomato cultivated on legume mulches ranged from 39 to 60% when compared to CT, while it rose from 45 to 69% when compared to NT depending on the N fertilization level. However, the trend of the NUE was similar among the legume mulches, while it was very different when tomato was grown on NTIR. In fact at N0 the NUE in NTIR was −31% and −59% when compared to NT and CT tomato, respectively, while it rose significantly at a higher N fertilization level and reached its highest value at N150 (37% and 30% in NT and CT, respectively). 4. Discussion In both years, the cover crop species emerged uniformly about 3 weeks after sowing. Although, the cover crop species grew regularly throughout the growing seasons (from September to May), hairy vetch and snail medic showed a significant reduction on aboveground biomass and N accumulation in the second year compared to the first year. This could be due to a different trend of temperatures during the coldest period of the year (from January to March, Fig. 1), especially in 2004 when the minimum temperatures dropped more frequently below 0 ◦ C. However, despite the unusually cold period, hairy vetch and subclover did not show frost damage, while in snail medic severe damage was observed on the above-ground biomass probably due to the low temperatures recorded in March. Several studies have pointed out that low temperatures could cause stress in hairy vetch and snail medic, which might directly affect the physiological processes, such as leaf area production and N fixation (Anughoho et al., 2009; Brandsaeter et al., 2008). However, in both years hairy vetch produced the highest amount of above-ground biomass and N accumulation compared

the other cover crop species, as shown in other studies (Campiglia et al., 2011; Brennan and Smith, 2005). Snail medic produced a high above-ground biomass in 2002/2003 similar to hairy vetch, while it showed a low above-ground biomass in 2004. Snail medic is known for its poor resistance to frost, especially during the reproductive period. In our experiment, it reached the flowering stage during the coldest period of the year. As expected the N accumulation was greater in the legume cover crops than in ryegrass (Hartwig and Ammon, 2002). Moreover, the legume cover crops significantly increased both the NO3 -N and the NH4 -N content in the upper soil layers (0–30 cm) at tomato transplanting compared to control treatments (conventional tillage and no tillage). Probably this is because they are less N efficient than ryegrass as catch crop (Ritter et al., 1998), and also due to the high N content of legume tissues that start to mineralize immediately after their suppression (Kramberger et al., 2009). The ryegrass cover crop, which is well known to be an efficient catch crop, showed the lowest soil NO3 -N values at tomato transplanting in the top layer of the soil (less to 34% compared to legume cover crops). This result is in agreement with the findings of Kuo and Sainju (1998), regarding grass cover crops which when seeded in late summer or autumn decrease soil NO3 -N and consequently reduce the risk of N leaching. Although an abundant above-ground biomass of cover crops was present at cover crop suppression, problems concerning tomato establishment into mulch strips were not observed, which is different to the findings of Teasdale et al. (2008) who found a reduction in the emergence of a sweet corn crop sown in a vetch mulch. Probably a dense layer of organic material could have exerted a strong suppressive action on corn seed in germination, due to both physical and chemical effects, while the tomato seedlings, did not seem to be affected by these negative mulch effects (Teasdale and Mohler, 1993). After cover crop suppression, the above-ground biomass left on the soil surface began to mineralize, even if leaving the organic mulch on undisturbed soil may slow down the soil drying process and maintain soil temperature lower compared to green manuring. With low soil temperatures the mineralization and nitrification processes could be delayed (Khaledian et al., 2010). Although these processes are affected by many factors (soil temperature, water content, soil characteristics, organic

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residue quality), Nakhone and Tabatabai (2008) reported that N release from organic residues could be strictly related to the C:N ratio. If the amount of N content in organic residues is larger than that required by the microbial biomass, there is a net mineralization with the release of inorganic N (Cabrera et al., 2005). Generally, ryegrass residues show an high C:N ratio which can cause a N immobilization and competition with the succeeding crop for the available N in the soil (Döring et al., 2005), while legume residues have a low C:N ratio and therefore rapidly mineralize and release a large amount of mineral N (Jensen et al., 2005). In our experiment, throughout the tomato crop cultivation, hairy vetch mulch released the highest amount of N and this supports the findings reported by Sainju et al. (2006), who observed a similar mineralization rate in hairy vetch residues in all tillage practices including no tillage. However all legume mulches released a large amount of N through the tomato crop leading to an increase of marketable fruit yield and tomato straw weight compared to conventional tillage and no tillage, as observed in a previous study (Campiglia et al., 2010b). Moreover, the tomato yield could have been greater in no tillage legume mulches also considering a large amount of green tomato fruits observed at tomato harvesting (data not shown). As reported by Thomas et al. (2001), cover crop mulches delayed the maturity of tomato fruits probably due to a high soil moisture and soil N content which delay and cause differences in tomato fruit ripening times (Parisi et al., 2006). This effect is undesired in processing tomatoes which are harvested at the same time (Doane et al., 2009), therefore it is necessary to optimize the time of harvest in order to improve the tomato yield, especially when the tomatoes are cultivated in legume mulches. Although the ryegrass cover crop produced a similar mulch biomass to legume cover crops, it released three times less N than hairy vetch mulch, and the tomatoes grown in no tillage ryegrass mulch showed the lowest tomato yield. Probably the large N quantity released from legume mulches is a key factor for improving the tomato yield (Unger, 1986), even if the organic mulch could have affected other factors such as soil temperatures and water dynamics (Coppens et al., 2007). However, N fertilization determined an increase in the tomato yield and tomato N uptake in all mulch treatments, therefore N supply from legume mulches did not seem to satisfy the tomato N demand. According to Zotarelli et al. (2009) the recommended N fertilization level for tomato crops in the Mediterranean areas is more than 220 kg N ha−1 . This implies that the 150 kg N fertilizer ha−1 , which is the maximum amount of N fertilization administered to the tomato crop in this study, was clearly not enough to induce maximal tomato yield. Replacing no tillage bare soil with the no tillage ryegrass mulch did not increase the amount of N accumulated in the tomato yield, while an increase of N was observed in tomatoes grown in NTHV, NTSC, and NTSM, even if the N increase did not reach the level of N present in the legume mulch biomass, as observed by Kramberger et al. (2009) in a corn crop. In fact the N accumulated in the cover crop above-ground biomass was not fully available for the tomato crop because a part of the N was still in the residues of the organic mulch after tomato harvesting, another part was probably available in the soil as mineral N, and a part enriched the soil organic pool (Tonitto et al., 2006). Consequently, after tomato harvesting the residual N was higher in legume mulch treatments compared to ryegrass mulch, conventional tillage, and no tillage treatments as observed by Gao et al. (2009). However, the higher amount of cover crop above-ground biomass and its N content observed in 2002/2003 compared to 2003/2004 could explain the difference in yield and N uptake on the following tomato crop, as reported by Sainju et al. (2002). The N content in the tomato fruits and tomato straw at tomato harvesting was similar to that reported by Tei et al. (2002), even if in conventional tillage, no tillage, and ryegrass mulch treatments the N content in marketable fruits tended to rise with the increase of the

N fertilization level (Zotarelli et al., 2009). Generally, the N content in marketable fruits was similar among the legume mulch treatments regardless the N fertilization level, while the tomato yield rose with the increase of the N fertilization rate. Probably, the soil mineral N during the vegetative period of the tomato was not sufficient for fulfilling the needs of the tomato crop, while it exceeded the tomato N demand during tomato fruit development and the ripening stage in legume mulch treatments (Scholberg et al., 2000). Therefore, when a no tillage legume mulch system is adopted it may be useful to apply a low N rate fertilizer, especially in the early stage of tomato crop when the mineralization of the cover crop aboveground biomass is slow (Nakhone and Tabatabai, 2008). However our results suggest that a no tillage system that includes organic legume mulches supplies N for the following crop, and therefore has the advantage of replacing N fertilizer in whole or in part, enabling us to reduce the amount of N fertilization without substantially reducing the tomato yield (Doane et al., 2009; Sainju et al., 2002). Furthermore, decreasing the rate of N fertilization could reduce the potential for N leaching into the groundwater (Sainju et al., 2001). Considering N use efficiency (NUE) of the tomato cultivated in organic muches, it was higher when compared to tomato cultivated in no tillage than when compared to tomato cultivated in conventional tillage, probably because the mineralization rate of the organic soil N pool is lower in no tillage than in the conventional tillage system (Sainju and Singh, 2001). However, NUE in legume mulched tomato decreased as the amount of N applied increased, as observed by Cassman et al. (2002). At tomato harvesting, the values of the apparent nitrogen remaining in the soil (ARNS) support the hypothesis that there is a large amount of N supplied to the crop which is not recovered by the tomato in the plots mulched with legumes. Although the ARNS allows only a simple comparison of the N input among treatments - in fact a N balance requires more information such as the N soil mineralization, N losses and N of rainfall and irrigation water - our results confirm that after the tomato harvesting in the legume mulched treatments there is a large amount of N-NO3 available in the soil even in unfertilized N plots. This outcome suggests that under no-till legume mulch systems it is necessary to enhance N recovery and reduce the potential N losses by manipulating the N supply and capturing the excess N before it is lost (Crews and Peoples, 2005). In this study the remaining N content in the residual mulch, and the soil mineral N after tomato harvesting, were still high in both experimental years which could cause high risks of NO3 -N leaching during the next wet season (Campiglia et al., 2011). Hartwig and Ammon (2002) suggest planting catch crops, such as grasses or cruciferae, which grow rapidly after the main crop lowering the potential for NO3 N leaching into groundwater during the wet season (Ritter et al., 1998). However, considering the high N content in the upper soil layer and the remaining N content in the organic mulch residues, it is also possible to consider an alternative and profitable use of this residual N by cultivating an autumn–winter vegetable, such as fennel or cabbage able to catch the soil N in order to reduce NO3 N leaching risks and to produce a commercial vegetable for the market.

5. Conclusions Winter legume cover crops converted into mulches are worth considering for their ability to support soil fertility in reduced tillage systems. In fact, compared to conventional tillage, direct transplanting into legume mulches of no-tillage tomato was positive considering a substantial increase in the tomato yield and tomato nitrogen uptake probably due to the high amount of accumulated N in the legume mulches, especially in hairy vetch. Therefore, legume winter cover crops and their mulches could

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