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Proper N fertilizer and irrigation management can reduce nitrate leaching while maintaining crop yield, which is critical to enhance the sustainability of vegetable production on soils with poor water and nutrient-holding capacities. This study evaluated different methods to measure nitrate leaching in mulched drip-irrigated zucchini, pepper, and tomato production systems. Fertigation rates were 145 and 217 kg N ha(-1) for zucchini; 192 and 288 kg N ha(-1) for pepper; and 208 and 312 kg N ha(-1) for tomato. Irrigation was either applied at a fixed daily rate or based on threshold values of soil moisture sensors placed in production beds. Ceramic suction cup lysimeters, subsurface drainage lysimeters and soil cores were used to access the interactive effects of N rate and irrigation management on N leaching. Irrigation treatments and N rate interaction effects on N leaching were significant for all crops. Applying N rates in excess of standard recommendations increased N leaching by 64, 59, and 32%, respectively, for pepper, tomato, and zucchini crops. Independent of the irrigation treatment or nitrogen rate, N leaching values measured from the ceramic cup lysimeter-based N leaching values were lower than the values from the drainage lysimeter and soil coring methods. However, overall nitrate concentration patterns were similar for all methods when the nitrate concentration and leached volume were relatively low.

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Lal et al., 1989). In Brazil, NT practices were introduced in the 1970s as a strategy to control soil erosion. Cur- In temperate regions, the adoption of no-tillage (NT) often stimu-rently, NT is being increasingly adopted in agricultural lates the sequestration of soil C and N and improves soil structural stability. The aim of this study was to investigate if NT has similar systems and to date the area under NT management is impacts on the stability of water-stable aggregates and C and N stabiliapproximately 22 Mha. soil temperature (Lal et al., 1978). These soil characteris- Oades, 1980; Carpenedo and Mielniczuk, 1990). Recently, subtropical soils there were rarely differences in thisThe lack of differences in C, N content, and C/N ratio across aggregateparameter between the two tillage systems. In contrast, increase in aggregation in the early years of NT adoption in tropical and subtropical regions compared with temperate regions. They suggested that this was a result of O xisols are the most common soil type in Brazil. the specific soil mineralogical characteristics (i.e., high The main soil characteristics of Oxisols are good Fe-and Al-oxide contents and a kaolinite dominated structural stability due to a clayey texture and a high clay mineralogy) of (sub)tropical soils such as Oxisols Fe and Al oxide content (Oades and Waters, 1991).and Ultisols. However, this suggestion was based on a The association of intense weathering conditions and synthesis of only five publications reporting data for Oxifrequent tillage have in many regions intensified soil sols. In addition, these five studies reported magnitudes erosion, resulting in a decrease in SOM, soil permeabilof responses in aggregation to NT that differed greatly. ity, water retention, soil aggregation, soil macro-and Consequently, little is known about the effect of NT on microfauna, and increasing the soil compaction and imsoil aggregation and its relationship with C stabilization balance of nutrients (Lynch and Painting, 1980; Tisdall for Oxisols. and Oades, 1980, 1982;Egashira et al., 1983;Lynch, 1984; In addition, different crops have different effects on soil aggregation and C accumulation: perennial grasses L. Zotarelli, Dep. of Soils, Universidade Federal Rural do Rio de due to their extensive root systems are more efficient in Janeiro-FAPERJ Seropé dica, 23890-000, RJ, Brazil; L. Zotarelli, K.soil aggregation than annual crops cultivated under CT Paustian, and J. Six, Natural Resource Ecology Laboratory, Colorado (Tisdall and Oades, 1980, 1982). Legume crops used as CT treatment disturbed the soil less at Passo Fundo than at The objective of this study was to determine the effect Londrina because only the winter cover crop was disk plowed, of different crop rotations and tillage on soil C and N whereas the summer crop was direct drilled. In the NT treataccumulation, the formation of water-stable aggregates, ments, both the summer and winter crops were direct drilled. and the quantity of aggregate-associated C at two sites At Passo ...