The sub-mountainous northern area (Potwar) in Punjab province of Pakistan is rainfed where six-month summer fallowing is commonly practiced to conserve moisture for winter wheat. Despite great deal of work worldwide, the controversy still remains for the best fallow management system. Crop residues, soil type, antecedent soil properties, type and depth of tillage and various climatic conditions may contribute to alter the soil characteristics. This field study was conducted during 2004-06 at three rainfall areas of Potwar viz. UAAR (high rainfall), Fateh Jang (medium rainfall) and Pindi Gheb (low rainfall). The objectives were to investigate impact of tillage systems and mulching on fallow efficiency, soil profile moisture dynamics, wheat production, nutrient removal and their economics.
Tillage and mulch treatments were employed in a split-plot design randomized in RCBD with four replications at start of summer fallow. Main plot treatments were: T1) Conventional cultivator (CC), T2) Subsoiler (SS), T3) Moldboard plow (MB) and T4) Minimum tillage (MT). Subplot treatments included a) no mulch and b) mulch of wheat straw @ 4 Mg ha-1. After fallow period, winter wheat (Triticum aestivum L) cv. Wafaq 2001 was grown repeatedly for two years.
Data indicated that volumetric water content at fallow end / wheat sowing was averagely 26 % lower under MT tillage than CC, SS and MB tillage systems. However, the differences vanished away after the winter rainfall during wheat crop. Fallow efficiency varied with sites and years. During 1st year, MT showed lower fallow efficiency by 6-15 % than other tillage systems. During 2nd year, MT became equivalent to other tillage systems at UAAR site. At Fateh Jang MT, CC and SS were similar, while MB showed 8-11 % higher fallow efficiency than others. Mulching showed slightly higher fallow efficiency compared to no mulch, however difference was non-significant. The fallow efficiency significantly influenced plant density but total biomass, grain yield and harvest index were not affected significantly, except the grain yield at UAAR site during 2004-05, was lower in MT by an average of 17 %. During 2005-06, MT produced conversely the highest yield of 3.10 Mg ha-1. Mulching produced higher grain yields by 13 % and 14 % in 1st and 2nd year at this site. WUE, total N and P uptake generally differed slightly or non-significantly among tillage treatments, however mulch improved total N and P uptake especially during the second year. The soil fertility parameters i.e. SOC, TSN, P and K both at wheat sowing and harvest did not show significant differences. In economic terms, MT without mulch gave the highest gross margins and benefit cost ratios of 3.81, 3.68 and 2.91 at UAAR, Fateh Jang and Pindi Gheb sites, respectively. The study concludes with the possibility of practicing resource conserving reduced tillage systems, without sacrificing grain yield, while avoiding the deleterious effects of long-term tillage in terms of potential erosion, soil quality and sustainability of agriculture.