Rice yield prediction from yield components and limiting factors

This article aims to quantify growth at field level in relation to crop status and soil properties in irrigated direct-seeded rice. Forty fields were selected in the Ebro Delta (Spain). Rice growth was monitored and soil properties measured. Yield was related to soil properties by a deductive process identifying the yield determining factors. First (i) yield components, then (ii) variables related to crop status, and finally (iii) soil properties were identified. To interrelate the different groups of variables, correlation analysis and an operational methodology of von Liebig's Law of the Minimum of the limiting factors were used. To quantify yield at field level, besides panicle and spikelet number, the fraction of necrotic grains, intensity of weed infestation and spatial heterogeneity within fields were necessary. Yield prediction accuracy from these five variables was very high, radj2=0.94. Four main factors limited rice growth: (i) potassium and (ii) zinc shortage, both with strong antagonism with sodium, (iii) plant establishment and (iv) length of the growing season. Yield prediction accuracy from these variables was moderately high, radj2=0.76. The longer the causal distance between yield and its determining factors, the lower the prediction accuracy. K and Zn deficiencies in the plant were mainly induced by soil salinity. The length of the growing period was primarily determined by temperature, but also by soil properties. Long growing cycle, homogeneity of plants per unit area, and adequate K and Zn levels in the plant were favored by high clay concentrations in the topsoi