Effects of tillage and biomass on soil quality and productivity of lowland rice cultivation by small scale farmers in North Eastern India

Intensive tillage-based production systems along with residue removal, grazing and/or burning of crop residues/biomass and poor nutrient replenishment through inadequate fertilizer and manure use are the major causes of soil degradation and unsustainable agriculture in hills of North Eastern India. Thus, a 4-year study (2003-07) was conducted during rainy (wet) seasons at Indian Council of Agricultural Research (ICAR) Research Complex for North Eastern Hill (NEH) Region, Umiam, India (950 m a.s.l.). Objective of the study was to assess the effect of different tillage systems (individual or combinations of spading, trampling and hand weeding) on rice (Oryza sativa L.) productivity and soil (Typic Paleudalf) quality under in-situ residue management in lowland conditions. Transplanting in manually weeded unpuddled field was termed no-till (NT). In comparison, individual or combinations of spading, trampling (one partial manual puddling to incorporate weeds) and weeding was termed minimum tillage (MT). Treatment involving the maximum tillage included 4 spading + 2 trampling + 2 weedings, and was termed the conventional tillage (CT). The latter is practiced widely by farmers' in the region. Nine tillage treatments were laid out in a Randomized Block Design (RBD) and replicated thrice in a fixed plot size of 5 m x 5 m. Increasing tillage intensity (combinations of spading along with trampling and weeding) increased grain yields. Agronomic yields obtained with 2 spading + 1 trampling + 1 weeding (MT option) was statistically (p = 0.05) similar to that under CT. In general, the weed biomass was more under NT and MT than CT, and also contributed 2-4, 0.8-2 and 0.78-1.9 times more N, P and K respectively, towards nutrient recycling than that under CT. However, the amount of N, P and K recycled through rice straw was more under CT than MT and NT. Weed biomass played a major role as a nutrient source in MT systems and contributed towards yield stabilization and improvement in soil quality. The soil organic carbon (25.2 g/kg), soil microbial biomass carbon (198.7 mu g/g dry soil) and dehydrogenase activity (25.84 mu g TPF/g dry soil) in NT were 11.5, 17 and 107%, respectively, more than those under CT. These parameters under MT systems were 6-13, 2-15 and 35-88%, respectively, more compared to those under CT. The bulk density (rho b) under CT (1.18 Mg/m(3)) was significantly higher than those observed under MT systems of only one spading or one trampling (1.15 Mg/m(3)). The net return was the highest with MT system comprising of 2 spading + 1 trampling + 2 weeding ($367.5/ha), and that was 25.5% higher than that with CT. The net return per dollar (NRP) invested decreased with increasing tillage intensity. In-situ rice residue retention along with weed biomass recycling (MT) for 4-years improved soil quality, reduced cost of production and stabilized productivity in a low-input marginal (marginal soil and small scale farmers) hill agriculture. (C) 2014 Elsevier B.V. All rights reserved.