Soil quality degradation associated with resources scarcity is the major concern for the sustainability of conventional rice-wheat system in South Asia. Replacement of conventional management practices with conservation agriculture (CA) is required to improve soil quality. A field experiment was conducted to assess the effect of CA on soil physical (bulk density, penetration resistance, infiltration) and chemical (N, P, K, S, micronutrients) properties after 4 years in North-West India. There were four scenarios (Sc) namely conventional rice-wheat cropping system (Sc1); partial CA-based rice-wheat-mungbean system (RWMS) (Sc2); CA-based RWMS (Sc3); and CA-based maize-wheat-mungbean (Sc4) system. Sc2 (1.52 Mg m−3) showed significantly lower soil bulk density (BD). In Sc3 and Sc4, soil penetration resistance (SPR) was reduced and infiltration was improved compared to Sc1. Soil organic C was significantly higher in Sc4 than Sc1. Available N was 33% and 68% higher at 0–15 cm depth in Sc3 and Sc4, respectively, than Sc1. DTPA extractable Zn and Mn were significantly higher under Sc3 and Sc4 compared to Sc1. Omission study showed 30% saving in N and 50% in K in wheat after four years. Therefore, CA improved soil properties and nutrient availability and have potential to reduce external fertilizer inputs in long run.

Diverse element toxicities (or deficiencies) that are exacerbated during waterlogging are proposed as a major reason why waterlogging tolerance at one site is often not replicated at another. Recommendations for germplasm improvement for waterlogging tolerance include use of inductively coupled plasma analyses of soils and plants.

involving use of NPK fertilizers alone and in combination with green manure (Sesbania bispinosa) or farmyard manure (FYM) in a rice-wheat cropping sequence. An attempt was made to evaluate the effect of the substitution of inorganic fertilizers with organic manures on yields of grain and nutrients, economy and soil fertility during 1997-98 and 1998-99. Application of NPK and its combination with green manuring and FYM increased the rice yield significantly. Applying inorganic fertilizers resulted in similar nitrogen use efficiency (NUE) in rice as compared with organic manures along with inorganic fertilizers, but NUE was increased in wheat by the residual effect of organic manures along with inorganic fertilizers. The responses of rice to the application of the full recommended amount of inorganic fertilizers (120 kg N, 26 kg P and 42 kg K/ha) and its combined use with green manure or 10 t/ha FYM and 150 % recommended amount (180 kg N, 39 kg P and 63 kg K/ha) were 2 . 98, 4 . 27, 4 . 10 and 3 . 54 t/ha, respectively. Further, with green manure or 10 t FYM/ha in combination with 50 % recommended amount, the mean rice yield (5 . 8 t/ha) was similar to the yield (5 . 5 t/ha) obtained from the 100 % NPK recommended treatment. Application of green manure or 10 t FYM/ha thus saved 60 kg N and 13 kg P/ha inorganic fertilizer in rice. The residual effect of green manure or FYM plus the full recommended fertilizer amount (120 kg N, 26 kg P and 42 kg K/ha) was significantly greater than that of the full recommended amount of fertilizer. Addition of green manure or FYM resulted in higher removal in crops, increase of soil N, P, K and organic C, and reduced soil pH. Application of the full recommended amount of fertilizer only maintained the N, P and K status in soil. Higher profit was obtained when inorganic fertilizer was combined with organic manures.

A long term field experiment was conducted for 8 years during 1994-2001 to evaluate the effect of N, P, K and Zn fertilizer use alone and in combination with gypsum, farmyard manure (FYM) and pressmud on changes in soil properties and yields of rice and wheat under continuous use of sodic irrigation water (residual sodium carbonate (RSC) 8.5 meq l À1 , and sodium adsorption ratio (SAR) 8.8 (m mol/l) 1/2 at Bhaini Majra experimental farm of Central Soil Salinity Research Institute, Karnal, India. Continuous use of fertilizer N alone (120 kg ha À1 ) or in combination with P and K significantly improved rice and wheat yields over control (no fertilizer). Phosphorus applied at the rate of 26 kg P ha À1 each to rice and wheat significantly improved the yields and led to a considerable build up in available soil P. When N alone was applied, available soil P and K declined from the initial level of 14.8 and 275 kg ha À1 to 8.5 and 250 kg ha À1 respectively. Potassium applied at a rate of 42 kg K ha À1 to both crops had no effect on yields. Response of rice to Zinc application occurred since 1997 when DTPA extractable Zn declined to 1.48 kg ha À1 from the initial level of 1.99 kg ha À1 . Farmyard manure 10 Mg ha À1 , gypsum 5 Mg ha À1 and pressmud 10 Mg ha À1 along with NPK fertilizer use significantly enhanced yields over NPK treatment alone. Continuous cropping with sodic water and inorganic fertilizer use for 8 years slightly decreased the soil pH e and SAR from the initial value of 8.6 and 29.0 to 8.50 and 18.7 respectively. However, treatments involving the use of gypsum, FYM and pressmud significantly decreased the soil pH and SAR over inorganic fertilizer treatments and control. Nitrogen, phosphorus and zinc uptake were far less than additions made by fertilizer. The actual soil N balance was much lower than the expected balance thereby indicating large losses of N from the soil. There was a negative potassium balance due to greater removal by the crops when compared to K additions. The results suggest that either gypsum or FYM/pressmud along with recommended dose of fertilizers must be used to sustain the productivity of rice -wheat system in areas having sodic ground water for irrigation.

Effects of waterlogging relative to drained conditions on grain yield were studied in relation to soil redox potentials and microelements (Fe and Mn) in soils from India and Western Australia, using waterlogging intolerant and tolerant varieties of wheat (Triticum aestivum L.) The grain yield of wheat decreased significantly with increasing duration of waterlogging in sodic soils. In Indian soils, soil redox potentials decreased sharply after waterlogging and were 150 and 210 mV at 10 days after waterlogging in alkali soil at pH 8.5 and pH 9.2, respectively. Two Australian soils were similarly reduced in redox potential with values of ~200 mV at 10 days after waterlogging, and redox potentials were further reduced to 100 mV and –50 mV for soils without and with added glucose, respectively, after 40 days of waterlogging. The Indian soils tended to be 2–10 times higher in DTPA-Mn than the Australian soils, whereas the Australian soils were up to 10 times higher in DTPA-Fe than the Indian soils. These increases were up to 10 and 60 times higher, respectively, than reported critical concentrations for wheat. After 21 days of waterlogging, the Indian soils were drained, and the re-aeration resulted in an increase in redox potential and a decrease in DTPA-Fe and -Mn in soil solutions, but this occurred slowly, taking 15–25 days. The results support the hypothesis that waterlogging tolerance is a product of tolerance to anoxia and microelement toxicities, and that these are both key factors limiting plant growth during and after waterlogging. These factors may also contribute to the large differences in screening wheat varieties for waterlogging tolerance in different soils.