Effects of crop residue incorporation on soil porperties and growth of subsequent crops

Abstract

A field study was carried out on four black earths to identify major factors influencing soil and plant growth traits when crop stubble was removed from or incorporated in the seedbed. The aim of the experiment was to identify important variables for further research. Wheat (Triticum aestivum), barley (Hordeum vulgare), sorghum (Sorghum bicolor) and sunflowers (Helianthus annuus) were used as both stubble species and test crops. A range of stubble quantities (596-11080 kg/ha) and qualities (C:N, C:P and C:S ratios of 24-148, 125-1600, and 182-1000 respectively) and periods of incorporation (up to 67 d) were involved. Data were analysed by paired t-tests and regression with combinations of factors. The technique used is discussed and its limitations examined. Due to logistical constraints, randomization was restricted, stubble removal technique was varied and a rotary hoe was used instead of conventional tillage machinery. Nitrate nitrogen (0- 10, 10-20 cm) was depressed when stubble was incorporated and this was related to the stubble C:N ratio. The effects on ammonium nitrogen (0-10 cm) and phosphorus (0-10 cm) were unclear. Stubble quantity was not well correlated. The importance of environmental factors during incorporation was unclear. During the inter-crop period, soil water content at 0-6 cm was significantly increased for up to 4 d after rainfall or irrigation when stubble was incorporated, and this was related to stubble quantity. It is suggested that stubble incorporation increased the volume of large soil pores which were filled by rain but subsequently dried rapidly. Likely short and long term effects of stubble incorporation on soil water are discussed. Incorporation of stubble did not consistently affect plant emergence or seedling vigour. Patchy stands in commercial crops may be due to isolated pockets of stubble formed by inadequate spreading of trash after harvesting or cultivation. Significant depressions of plant growth occurred later at sites 1 and 2 (wheat and barley) but not at sites 3 and 4 (sorghum and sunflowers). These depressions were primarily related to soil nitrate nitrogen (0-10, 10-20 cm) which was depressed by the wide C: N ratio of added stubble. Plant growth was positively correlated with stubble quantity at sites 2 and 3, and this was related to the sulfur and phosphorus contents of the stubble, respectively.