Effect of Composted Organic Matter on Boron Uptake by Plants

Boron uptake by plants is controlled by the B level in soil solution rather than the total B content in soil. The affinity of organic matter for B can affect B uptake by plants because of changing B concentration in soil solution. The role of soil organic matter content on B soil solution concentration and uptake by bell pepper ( Capsicum frutescens L.) were studied. The organic matter used was mature compost (COM), produced from the solid fraction of separated straw‐containing cattle manure. Plants were grown in five soil–sand–COM mixtures containing 0, 1, 3, 6, or 10% COM by weight. Four levels of B were applied. The soil was analyzed for B content at the beginning of the experiment and at harvest. Boron concentration in the leaves was determined 45 d from planting. Boron concentration in the soil solution at the beginning of the experiment decreased with increasing levels of COM. This decrease was most prominent at high levels of B application. The effect of the COM level on leaf B concentration was also prominent at high B application rates, with increasing levels of COM resulting in less B in the leaf tissues. Boron concentration in the leaves was highly significantly correlated ( r 2 = 0.88) with the B concentration adjusted in the soil solution. This correlation coefficient was further improved ( r 2 = 0.98) when B concentration in the soil solution was calculated using a B adsorption model. The results presented herein indicate that organic matter plays an important role in controlling B concentration in the soil solution, and that it has a prominent effect on reducing B uptake by plants.